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9003 






Bureau of Mines Information Circular/1985 



Effect of Turbulence on Vortex-Shedding 
Air-Velocity Transducers 



By A. F. Cohen 




UNITED STATES DEPARTMENT OF THE INTERIOR 



CD 

c 

ID 

m 
> 

c 



75 



'Wines 75th av^ 



Information Circular 9003 



Effect of Turbulence on Vortex-Shedding 
Air- Velocity Transducers 



By A. F. Cohen 



UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



# 



ofo 



\N^. 



AD' 




Library of Congress Cataloging in Publication Data: 



Cohen, A. F 4 

Effect of turbulence on vortex-shedding air-velocity transducers. 

(Information circular ; 9003) 

Bibliography: p. 11. 

Supt. of Docs, no.: I 28.27:9003. 

1. Mine ventilation — Equipment and supplies. 2. Air flow— Measure- 
ment— Instrument. 3. Turbulence. 4. Coal mines and mining— Safety 
measures. I. Title. II. Series: Information circular (United States. 
Bureau of Mines) ; 9003. 



TN295.U4 [TN301] 622s [622\8l 84-600145 



^T|) CONTENTS 

-^Abstract 1 

—^Introduction 1 

-^Mi ne turbulence 2 

~ < ^Eurrent investigation 2 

* Principle of operation 3 

Wind tunnel and turbulence grid and T.I. characterization 3 

CJ Calibration of BA4 and VA216B 5 

BA4 experiments 7 

Experimental data 7 

Additional data 8 

VA216B experiments 10 

Further work 10 

Conclusions 10 

References 11 

Appendix. — Specific BA4 and VA216 data 12 

ILLUSTRATIONS 

1 . BA4 transducer with horn attached 3 

2 . Cloverleaf grid 4 

3. Free-stream turbulence intensity using cloverleaf grid for turbulence 

generation 5 

4. BA4 calibrations..... 6 

5. VA216B calibration 6 

6. VA216B transducer 6 

7. Ratio of BA4 (corrected for calibration) to HW versus X/M 7 

8. Relative ratio of BA4 (corrected for calibration) to HW versus X/M 8 

9. Ratio of VA216B (corrected for calibration) to HW versus X/M 10 

10. Relative ratio of VA216B (corrected for calibration) to HW versus X/M. . . . 10 

A-l. Pulse frequency versus true velocity for VA216..... 13 

TABLES 

1. Free-stream T. I. downstream of grid using BA4 9061 4 

2. Calibration of BAA 9061, horn removed 5 

3. Calibration of VA216B 7 

4. BA4 9061 ratio of Uba4/Uhw as function of mean speed (HW) for two values 

of X/M, horn removed 8 

5. BA4 9061 with air velocity approximately constant and X/M varied (BA4 

downstream of cloverleaf grid) 9 

3 ; A-l. Calibration 1 of BA4 9050, horn on 12 

A-2. Calibration 2 of BA4 9050, horn on 12 

A-3. Calibration of BA4 9050, horn removed 13 

A-4. Calibration of BA4 9061, horn on 13 

J A-5. Additional calibration of BA4 9061, scale 1, horn on 13 

3 





UNIT OF MEASURE ABBREVIATIONS 




ft 


foot in 


inch 


f t/min 


foot per minute m/s 


meter per second 


Hz 


hertz 





EFFECT OF TURBULENCE ON VORTEX-SHEDDING AIR-VELOCITY TRANSDUCERS 

By A. F. Cohen 1 



ABSTRACT 

When location guidelines are followed in choosing sites for fixed- 
point velocity transducers for use in underground coal mine monitoring, 
mine air turbulence intensities <11% are generally expected at those 
sites. The objective of this Bureau of Mines investigation to determine 
the effect of turbulence intensities <11% on vortex shedding sensors and 
transducers. 

Measurements were made at velocity levels of interest for underground 
coal mine monitoring use ("200, «500, «1,000, «1,500 f t/min) . The ef- 
fect of grid-produced turbulence intensities (2% to «14%) on the output 
of vortex-shedding air-velocity transducers was less than ±10%. 

INTRODUCTION 

Underground coal mine air moving at velocities of approximately 200 to 
1,500 f t/min is turbulent and the presence of such turbulence may affect 
the output of air-velocity sensors or transducers. Interim performance 
specifications for fixed-point air-velocity transducers 2 used with the 
Bureau of Mines Intrinsically Safe Mine Monitoring System (ISMMS) recom- 
mend 90% accuracy in the velocity range 200 to 1,500 ft/ min. There- 
fore, the Pittsburgh Research Center, in cooperation with the National 
Bureau of Standards (NBS), investigated the effect of turbulence inten- 
sity (T.I.) 3 on transducer output to determine whether turbulence inten- 
sity had a large (>30%) effect or a relatively small (<10%) effect at 
mine turbulence levels corresponding to optimal transducer locations in 
U.S. underground coal mine airways. 

'Physicist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 

^A transducer is a packaged component that is connected to a source of power and 
delivers an output signal related to the variable being measured. The package con- 
tains a sensor, signal conditioning circuits, and power conditioning circuits. The 
sensor is a device that produces an electrical signal in response to a specific 
parameter, such as air velocity. 

3 RMS average of turbulent component of velocity , 
T • 1 • — n . — u/U. 

Average velocity 



MINE TURBULENCE 



A literature search of expected levels 
of turbulence in underground coal mines 
produced few references. Teale Q_) 4 re- 
ported that mine air fluctuations caused 
vane anemometers to read high. Teale' s 
experiments with vane anemometers were 
conducted in an experimental underground 
mine gallery of rectangular cross sec- 
tion, 4 ft 9 in by 6 ft 4 in. His ex- 
periments indicated that the amount of 
overestimate of air velocity by vane 
anemometers was related to the amplitude 
of fluctuation^ of the air; the greater 
the amplitude of fluctuation, the greater 
the overestimate of velocity. An ampli- 
tude of fluctuation of 30% corresponded 
to an overestimate of air velocity (by 
vane anemometer) of 17%. 

Turbulence intensity measurements were 
performed under a Bureau-sponsored con- 
tract at the Bureau's Safety Research 
Coal Mine, Bruceton, PA, at a location 
consistent with air velocity transducer 
site guidelines (2^, p. 32). At these 
locations T.I. was determined at 26 
equally distributed points representative 
of «75% of the total («6 ft high by 18 ft 
wide) cross sectional area (bottommost 
area near floor was not sampled nor was 
one side, adjacent to the rib). The 
average of the 26 T.I.'s measured was 
«11%. The average T.I. of the center 
section of the airway (representing four 
data points) was 6% to 7%. Average air 



velocity through the cross section was 
«200 ft/min. (Turbulence intensity is 
one descriptor of turbulence; spectral 
content and turbulence scale are others.) 

In 1978, a research project at the 
Bureau's Experimental Mine, Bruceton, PA, 
obtained T.I. data (on a vertical center 
line) as a function of distance from the 
roof to the center of the airway cross 
section (roof to floor distance was 8 
ft). In that cross section, T.I. at the 
center was »3.5% (velocity was 155 
ft/min); at 0.5 ft/min from the roof, 
T.I. was 9.4% (velocity was "96 ft/min); 
at 1 ft from the roof, T.I. was 8% 
(velocity was 125 ft/min). In this case, 
T.I. varied monotonically with distance 
from the roof to the center of the cross 
section. 

At another location in the same mine 
(distance from roof to floor was «7 ft) , 
at the center of the cross section, T.I. 
was «9.5% (velocity was 165 ft/min); at 
0.5 ft from roof, T.I. was 7.3% (velocity 
was «110 ft/min); at 1 ft from the roof, 
T.I. was «6% (velocity was 125 ft/min); 
and at 1.5 ft from roof, T.I. was «5% 
(minimum value) and velocity was "135 
ft/min. On the basis of the above infor- 
mation, T.I.'s up to approximately 11% 
represent a reasonable range for studying 
the effect of mine T.I. on output of the 
air-velocity transducer. 



CURRENT INVESTIGATION 



The current investigation involves two 
types of vortex-shedding transducers: 
the BA4 Air Velocity Monitor (model MRD 
69340) by Technitron, Surrey England; and 
the VA216B Air Draft Sensor by J-Tec As- 
sociates, Cedar Rapids, IA. 

The BA4 is a system for measuring, in- 
dicating, and recording air velocity. It 

^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendix. 

^Amplitude of fluctuation 

J_ Maximum velocity - minimum velocity . 

2 Mean velocity 



includes the transducer, a control unit, 
a strip chart recorder, and a battery- 
power unit. The transducer includes the 
sensor, which detects vortices created by 
a fixed-dimension strut by means of ul- 
trasonics and electronic circuits; the 
control unit provides electrical power to 
the transducer and access to the output 
signal from the transducer. 

The VA216B is a transducer that in- 
cludes a sensor that detects vortices 
created by a fixed-dimension strut by 
means of ultrasonics and the electronic 
circuits. The VA216B is in use in the 



Bureau's ISMMS (_3 ) . An earlier model, 
the VA216, was very mineworthy under nor- 
mal mine operating conditions (4^ p. 3). 

The original patent for ultrasonically 
detecting vortex shedding is held by J- 
Tec, so some similarities between the J- 
Tec and the BA4 might be expected; how- 
ever, there are notable differences. For 
example, the VA216B sensor strut cross 
section is cylindrical, whereas that of 
the BA4 is triangular; also, the BA4 
transducer includes a shieldlike attach- 
ment (horn), as shown in figure 1. 

PRINCIPLE OF OPERATION 

Vortices are formed in air passing 
around an object such as a cylinder. The 
rate of vortex formation (the frequency) 
is proportional to air speed. A plot of 
pulse frequency versus velocity for the 
VA216 transducer (_5) is shown in appendix 
figure A-l. The number of vortices 
formed (or shed by the cylindrical strut) 
per unit time downwind from the cylinder 
are counted ultrasonically using a trans- 
mitter and receiver downstream of the 
vortex-shedding cylinder. The frequency 
of vortices shed is independent of en- 
vironmental factors such as temperature, 
humidity, and presence of dust, as long 
as the cross section of the vortex shed- 
ding element (cylinder, for example) re- 
mains unchanged. 



An experiment under a Bureau contract 
(J_, p. 56) indicated that turbulence 
(T.I. estimated between 20% and 30% at a 
simulated mine split using a wind tunnel) 
resulted in an overestimate of air 
velocity of more than 30% as measured by 
the VA216B. A hot film anemometer was 
used as the air-velocity-control instru- 
ment in the proximity of the VA216B. 

WIND TUNNEL AND TURBULENCE GRID 
AND T.I. CHARACTERIZATION 

The NBS 5- by 7-ft test section of the 
dual test section wind tunnel was used 
for turbulence tests on the BA4 9061, and 
the VA216B. Turbulence intensities up to 
and in excess of 10% could be obtained 
using aluminum "cloverleaf" decorative 
panels in a specially constructed grid 
(fig. 2A) . This grid was backed by a 
second grid identified as an NBS 1-1/4-in 
woven mesh grid made of 1/4-in-diameter 
cylindrical rods for support (fig. 25). 

The distance between adjacent centers 
of the cloverleaf openings is 0.50 in. 
Therefore, it is assumed that 0.50 in. is 
the mesh, M, for the cloverleaf grid. 
Also, X is the distance, in inches, from 
the grid to the center of the cross sec- 
tion of the triangular vortex-shedding 
strut of the BA4. The turbulence inten- 
sity ratio, u'/U, was measured as a 
function of X/M for four mean stream 





FIGURE 1. - BA4 transducer with horn attached. A, Overall view; B, front view, showing sensor 
inside horn. 














s»>>***»* '- 








FIGURE 2;> - Cloverleaf grid* ^4, Upstream side of cloverleaf grid; B, downstream side of cloverleaf 
grid with l-l/4=in NBS grid in front (appearing as small, connected squares). Panel B shows BA4 with- 
out horn (bottom of photograph) and hot-wire anemometer (directly above). 



velocities , where U is the mean stream 
velocity and u* is the RMS average of ve- 
locity fluctuations about the mean veloc- 
ity. The data, in the order obtained, 
are presented in table 1, and a plot of 
the data is presented in figure 3. 



The turbulence intensity, u'/U, pro- 
duced by the grid at a given distance, 
expressed in units of X/M from the 
screen, is velocity dependent, especially 
at the lower values of X/M, where the 
turbulence intensities are the highest 



TABLE 1. - Free-stream T. I. downstream of grid using BA4 9061 
(M = 1/2 in; 5- by 7-ft wind tunnel) 



U «1,000 


ft/min 


U «500 ft/min 


U «1,500 


ft/min 


U «200 ft/min 


T.I 


X/M 


T.I. 


X/M 


T.I. 


X/M 


T.I. 


X/M 


0.0737 


32 


0.191 


12 


0.0275 


120 


0.1700 


12 


.0617 


40 


.140 


16 


.0320 


96 


.1237 


16 


.0515 


48 


.111 


20 


.0382 


84 


.1014 


20 


.0427 


60 


.0900 


24 


.0424 


72 


.079 


24 


.0352 


72 


.0672 


32 


.0433 


60 


.059 


32 


.0338 


84 


.0536 


40 


.0521 


48 


.048 


40 


.0303 


96 


.0470 


48 


.0576 


40 


.043 


48 


.0261 


120 


.0426 


60 


.0711 


32 


.037 


60 


.0969 


24 


.0403 


72 


.0922 


24 


.0344 


72 


.1467 


16 


.0364 


84 


.1133 


20 


.0325 


84 


.1974 


12 


.0346 


96 


.1476 


16 


.0262 


96 


.1173 


20 


.0276 


120 


.2057 


12 


.0223 


120 



20 


a 

• 










1 


1 


1 


1 1 1 1 1 


18 


o 
















KEY 
o =200 ft/min 


16 


- 
















• =500 ft/min 


14 


- 


B 

• 














a =1,000 ft/min 
d =1,500 ft/min 


12 


- 


o 


A 

8 












- 


10 


- 




O 


A 

3 










- 


08 
06 
04 
no 






i 


O 


6 

• 


1 


A 

□ 
• 
O 

I 


H 

• 

o 

1 


i 

o 


B B 

6 ^ I 1 



TABLE 2. - Calibration of BA4 9061, 
horn removed 1 » 2 



10 20 30 40 50 60 70 80 90 I00 IIO 1 20 
DISTANCE FROM GRID, X/M 

FIGURE 3. - Free-stream turbulence intensity 
using cfoverfeaf grid for turbulence generation. 
M = 0.50 in. 

(fig. 3). A range of turbulence inten- 
sity of 2% to «14% was realized with the 
grid in experiments to be described in 
this report. 

CALIBRATION OF BA4 AND VA216B 

A linearized hot-wire anemometer (LHWA) 
was used as a reference velocity-measur- 
ing device whose mean indication is 
assumed to be stable and unaffected 
by high turbulence intensities. Measure- 
ments were performed in the NBS 5- by 7- 
ft wind tunnel. The LHWA anemometer, in 
turn, was calibrated in the NBS low- 
velocity wind tunnel using a laser veloc- 
imeter. The low-velocity wind tunnel is 
the same wind tunnel in which the BA4 
system was calibrated in 1982. Appendix 
tables A-l through A-5 show the calibra- 
tion data obtained in 1982 for the BA4 
systems 9050 and 9061. A plot of the 0° 
yaw, 0° pitch calibration data for BA4 
9050 with horn on (normal state) and also 
with horn removed is shown in figure 4. 
The BA4 9061 without horn was recently 
calibrated in the NBS low-velocity wind 
tunnel using a laser velocimeter as stan- 
dard. These data appear in table 2 and 
are plotted in figure 4. 



True airspeed 
(V + ), m/s 



Indicated 
airspeed, 
(Vj), m/s 



SCALE 1 



SCALE 2 



SCALE 3 



V+/V, 



1.075 


1.00 


1.08 


.9841 


.90 


1.24 


.8722 


.80 


1.09 


.7696 


.70 


1.10 


.6472 


.60 


1.08 


.5335 


.50 


1.07 


.4632 


.40 


1.16 


.3264 


.30 


1.09 


.2657 


.22 


1.21 


1.006 


.80 


1.26 


1.248 


1.20 


1.04 


1.518 


1.50 


1.01 


1.696 


1.70 


.998 


1.971 


2.00 


.996 



2.023 


2.00 


1.01 


1.578 


1.50 


1.05 


1.096 


1.00 


1.10 


.5907 


.50 


1.18 


2.494 


2.50 


.998 


2.917 


3.00 


.972 


3.392 


3.50 


.969 


3.869 


4.00 


.967 


4.349 


4.50 


.966 


4.837 


5.00 


.967 



4.888 


5.00 


0.978 


5.757 


6.00 


.960 


6.909 


7.00 


.987 


7.901 


8.00 


.988 


9.004 


9.00 


1.000 


10.14 


10.00 


1.014 


3.867 


4.00 


.966 


2.916 


3.00 


.972 


2.012 


2.00 


1.006 


1.123 


1.00 


1.123 



'The BA4 instrument seal 
meters per second, hence pre 
data of the BA4 and figures 
the data are in those units. 

2 Data are presented in 
tained and indicates effect 
airspeed. 



es are in 
sentation of 
illustrating 

order ob- 
of changing 




FIGURE 4. - BA4 calibrations. 



| 1,000 





200 400 600 800 1,000 1,200 1,400 1,600 1,800 
V(, tt/min 

FIGURE 5.- VA216B calibration. 



FIGURE 6. - VA216B transducer. A, Overall 
view; B, closeup, showing transmitter {l), cylin- 
drical strut [2), and receiver (3). 



The LHWA is in a fixed position ver- 
tically above and in the same plane as 
the sensing element (the strut) of the 
BA4 9061 and is maintained in the same 
plane as the BA4 strut as X/M is varied. 
Movable supports were employed to vary X, 
hence X/M, yet keep a constant distance 
(18-1/4 in) between the LHWA and the BA4. 
Fig. 25 shows the BA4 without horn in the 
5- by 7-ft test section of the wind 
tunnel. 

A similar arrangement was used for the 
VA216B measurements. Calibration data of 
the VA216B are shown in table 3 and fig- 
ure 5. Figure 6 shows the VA216B. 



TABLE 3. - Calibration of 
VA216B, feet per minute 



V, 



i 



56.21 


0.00 


153.6 


73.8 


218.3 


220.8 


300.6 


345.6 


398.0 


450.6 


598.1 


730.8 


792.4 


943.2 


990.6 


1,111 


1,235 


1,331 


1,478 


1,547 


1,737 


1,769 


114.3 


96.0 


139.3 


78.0 



BA4 EXPERIMENTS 



EXPERIMENTAL DATA 

For the first experiments with X/M con- 
stant, BA4 9061 transducer outputs and 
concurrent LHWA readings were obtained at 
four velocity levels. Using the calibra- 
tion data, calibration corrections to the 
BA4 output were incorporated in obtaining 
the following ratio: BA4 (corrected) to 
LHWA designated as BA4 (corrected) to HW 
in the graphical presentations. 

The velocity levels («200, «500, 
« 1,000, « 1,500 ft/min) are not precisely 
reproduced at a given X/M as the sequenc- 
ing of measurements at different veloci- 
ties is made. 

The appreciable increase in BA4/HW out- 
put (fig. 7) at X/M <30 is attributed to 
the proximity to the grid of the BA4 horn 
rather than a turbulence intensity de- 
pendence of the vortex shedding sensor; 
i.e., if the BA4 9061 with horn was 
placed in a mine away from obstructions 
but where turbulence intensities of the 
order of 8% to 10% existed, the antici- 
pated effect would be approximately the 
same as on the BA4 9061 without horn. 
One test confirming this assumption con- 
sisted of removing the horn and deter- 
mining the ratio of BA4 (corrected) to 
LHWA at an X/M <30 (cloverleaf grid). In 



figure 7, data without the horn are shown 
for X/M = 18 and also for X/M = 84; the 
ratio BA4 (corrected) to LHWA output is 
largely reduced at X/M = 18 , compared to 
the case with the horn attached. The 
data without the horn are presented in 
table 4, and averages of the data without 
horn are plotted in figure 7. 



1.6 
1.5 
1.4 
1.3 
1.2 
I.I 
1.0 
.9 
.8 



KEY 

Without horn 
V=200 ft/min 
V=500 ft/min 
V=l,000 ft/min 
V=l,500 ft/min 




=1,500 

x 
=1,000 ft/min 



= 1,000 ft /mm 
= 1,500 ft/min' 
=200ft/min / 
=500 ft/min' 



10 20 30 40 50 60 70 80 90 
DISTANCE FROM 6RID, X/M 

FIGURE 7. - Ratio of BA4 (corrected for 
calibration) to HW versus X/M. 



TABLE 4. - BA4 9061 ratio of U BA4 /U HW 
as function of mean speed (HW) for 
two values of X/M, horn removed 



U HW , ft/min 1 



U BA4/ U HW 



X/M = 18 



U BA4 
(corrected) 



nhm. 



206 


0.93 


1.00 


498 


1.14 


1.14 


1,513 


.94 


.93 


969 


.91 


.88 


491 


1.08 


1.08 


206 


.98 


1.05 


973 


.90 


.87 


973 


.91 


.81 


1,497 


.95 


.94 


501 


1.13 


1.13 


208 


.97 


1.04 


1,493 


.95 


.94 


928 


.95 


.95 


515 


1.14 


1.14 


Average: 2 






«200 


.96 


1.03 


«500 


1.12 


1.12 


«1,000 


.92 


.875 


»1,500 


.95 


.94 



X/M = 84 



567 


0.92 


0.92 


195 


.83 


.89 


969 


.91 


.88 


1,491 


.91 


.90 


193 


.82 


.88 


490 


.93 


.93 


994 


.91 


.88 


1,492 


.92 


.91 


199 


.87 


.94 


492 


.97 


.97 


975 


.93 


.90 


1,518 


.92 


.91 


Average: 2 






«200 


.84 


.90 


«500 


.93 


.94 


«1,000 


.92 


.92 


«1,500 


.92 


.91 



and indicate effect of changing speed. 
2 Average velocity levels of above data. 



ADDITIONAL DATA 

Additional data with the BA4 9061 was 
obtained in a different manner than 
shown in figure 7. In figure 8, the air 



velocity in the wind tunnel was held 
quite constant (see table 5) , and the 
effect of air turbulence intensity of 
different values on the BA4 output was 
examined; all else remained constant. 
This was done by measuring the BA4-to-HW 
ratios for different X/M, velocity re- 
maining constant. 

For the present, these data (fig. 8) 
should be considered "relative" data. 
After figure 7 experiments, the turbu- 
lence grid had to be removed from the 
tunnel to make the tunnel available for 
use by others. When the experiment was 
resumed, lower values of BA4 (corrected) 
to HW were obtained. These lowered val- 
ues are in part attributable to a change 
in the HW anemometer calibration. In any 
case, the effect of grid-produced turbu- 
lence does not appreciably affect the 
output of the BA4 vortex shedding device 
(effect is <±10% about the mean BA4 (cor- 
rected) /HW) between T.I. = 2% and «12% at 
either 200 fpm or 500 fpm velocity level. 

Figure 8 includes BA4 9061 data with 
horn attached and with horn removed at 
air velocities of approximately 200 and 
500 ft/min. With horn attached, keeping 
the velocity constant and altering X/M 
results in the plots of the (relative) 
ratio BA4 (corrected for 
to HW versus X/M. The 
in output (fig. 8) at 
500 ft/min for X/M <20 
are very comparable to those in figure 7 
(horn attached) and are attributed to the 
horn's proximity to the grid. 



1.5 



BA calibration) 
large increase 
both 200 and 

(horn attached) 



1.4 



1.0 



KEY 
l A =200 ft/min 

\o =500 ft/min 
/«=500ft/min (horn removed) 

ln=200ft/min (horn removed) 




"10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 
DISTANCE, X/M 

FIGURE 8. - Relative ratio of BA4 (corrected 
for calibration) to HW versus X/M. 



TABLE 5. - BA4 9061 with air velocity approximately constant and X/M 
varied (BA4 downstream of cloverleaf grid) 



U HW» , 






BA4 


U HW> , 






BA4 


ft/min 1 


X/M 


BA4/HW 


(corrected)/ 
HW 


ft/min 1 


X/M 


BA4/HW 


(corrected)/ 
HW 


SB 


200 ft/min, i N 


SB 


500 ft/min, HORN ON 


189 


14 


1.24 


1.39 


513 


28 


0.855 


0.829 


193 


16 


1.02 


1.14 


514 


13 


1.48 


1.44 


206 


18 


.959 


1.06 


519 


16 


1.20 


1.16 


204 


20 


.878 


.975 


522 


18 


1.07 


1.04 


208 


22 


.844 


1.03 


518 


20 


.971 


.942 


209 


24 


.805 


.886 


516 


48 


.850 


.825 


207 


28 


.794 


.873 


512 


40 


.840 


.815 


208 


32 


.775 


.853 


511 


48 


.823 


.798 


213 


40 


.748 


.823 


507 


130 


.812 


.788 


208 


48 


.721 


.793 


512 


160 


.803 


.780 


209 


60 


.718 


.790 


506 


28 


.849 


.823 


206 


84 


.722 


.789 


507 


14 


1.48 


1.44 


205 


130 


.740 


.821 


514 


60 


.783 


.760 


204 


160 


.761 


.845 


515 


22 


.870 


.844 


213 


28 


.774 


.851 


501 


160 


.803 


.780 


213 


14 


1.24 


.36 


506 


40 


.800 


.776 


197 


22 


.843 


1.936 


502 


28 


.820 


.795 


205 


60 


.714 


.793 


502 


16 


1.15 


1.12 


207 


160 


.751 


.832 










206 


40 


.736 


.816 










202 


28 


.770 


.855 










«2 


00 ft 


/min, H 


ORN OFF 


«500 ft/min, HORN OFF 


191 


14 


0.850 


0.913 


504 


16 


0.835 


0.835 


202 


16 


.815 


.876 


487 


14 


.882 


.882 


199 


18 


.826 


.888 


496 


18 


.848 


.848 


195 


20 


.836 


.899 


514 


20 


.819 


.819 


198 


22 


.842 


.905 


520 


22 


.791 


.791 


203 


14 


.821 


.883 


521 


24 


.790 


.790 


194 


28 


.755 


.812 


514 


32 


.783 


.783 


201 


32 


.774 


.832 


522 


40 


.779 


.779 


204 


40 


.737 


.792 


517 


48 


.779 


.779 


203 


48 


.739 


.794 


507 


60 


.794 


.794 


197 


50 


.772 


.830 


503 


84 


.801 


.801 


199 


84 


.781 


.840 


505 


130 


.797 


.797 


204 


130 


.778 


.837 


512 


160 


.804 


.804 


207 


160 


.779 


.837 


514 


28 


.782 


.782 


200 


28 


.759 


.816 











Data are presented in order obtained and indicate effect of changing 



airspeed, 



With the horn removed, at X/M <30, 
the relative ratio of BA4 (corrected 
for BA4 calibration) to HW remains near- 
ly constant (T.I. increasing from «6% 
to 12% between X/M = 30 to X/M = 14, 
respectively) . 



The most important finding is that 
T.I.'s of 2% to "14% employed in this in- 
vestigation affect the output of the BA4 
very little (less than ±10% about the 
mean BA4/HW output) at each of the veloc- 
ity levels investigated. 



10 



VA216B EXPERIMENTS 



As with the BA4 system, the first ex- 
periments with the VA216B transducer were 
conducted at constant X/M and the veloc- 
ity level was varied (four levels). The 
data were obtained a few days after the 
data of figure 7 (BA4 system) and are 
shown in figure 9. The results are not 
unlike those with the BA4 system ob- 
tained in a similar manner (not absolute 
equilibrium) . 

Later, data were obtained with the 
VA216B in the same way and under compara- 
ble conditions as those of figure 8 (BA4 
system). Figure 10 shows these VA216B 
data in which a specific velocity was 
held constant for an extended period and 
X/M was varied. The effect of varying 
only the T.I. is indicated. 

For a given velocity level (e.g., 1,500 
f t/min) , the variations in VA216B (cor- 
rected) to HW over the range of X/M (14 
to 160) corresponding to T.I. (12% to 2%) 
are less than ±10% about the mean [VA216B 
( corrected) /HW] value at 1,500 f t/min. 

When used as a fixed-point transducer 
for a mine monitoring system such as the 
Bureau's ISMMS, where a given velocity 
level is maintained for days or weeks , 



1.4 
1.3 
1.2 
I.I h 



m 

2 i.o 



.9 





1 


1 


i ' l 

KEY 


i i i 


1 


- 




o 


=200 ft/min 




_ 






• 


=500 ft/min 






_ 


O o 


A 


= 1,000 ft/min 




_ 




6 


D 


-1,500 ft/min 






— 




8 

D 


8 
8 




— 




J 


A 


o 

o 


j 










8 






1 


i 


i,i, 


i 1 


< 



20 40 60 80 

DISTANCE, X/M 



100 



120 



FIGURE 9. - Ratio of VA216B (corrected for 
calibration) to HW versus X/M. 



5 1.2 



KEY 
o =200 ft/mm 
• =500 ft/min 
a =1,000 ft/mm 
a =1,500 fl/min 




s 



20 



60 80 100 

DISTANCE, X/M 



FIGURE 10. - Relative ratio of VA216B (cor- 
rected for calibration) to HW versus X/M. 

the VA216B output changes due to T.I.'s 
up to 11% would be small (<±10%). 



FURTHER WORK 



The spectral content of the grid- 
produced turbulence is under investiga- 
tion. The effect of turbulence scale on 
vortex-shedding transducers has not been 
measured but was considered in the choice 



of grid used in experiments reported 
here. Turbulence scale and low-frequency 
fluctuations and/or pulsations of the air 
in mines has yet to be characterized. 



CONCLUSIONS 



The most important finding of the pres- 
ent investigation is that grid-produced 
T.I.'s of 2% to K 14% employed in this in- 
vestigation affect the output of the BA4 
system very little — on the order of ±10% 
or less over the range of conditions 
tested. 



Similarly, grid-produced T.I.'s (ap- 
proximately 2% to 14%) affect the out- 
put of a VA216B transducer less than 
±10% at velocity levels 200 to 1,500 
ft/min. 



11 



REFERENCES 



1. Teale, R. The Accuracy of Vane An- 
emometers in the Measurement of Mine Air- 
flow. Nat. Coal Board MRE Rep. 2040, 
1956, 20 pp. 

2. Kohler, J. An Evaluation of the 
Air Velocity Sensing Unit in the Bureau 
of Mines Remote Monitoring System con- 
tract J0308027, Ketron, Inc.). Mar. 1, 
1982, 57 pp; available from A. F. Cohen, 
BuMines, Pittsburgh, PA. 

3. Fisher, T. J. , and M. Uhler. Re- 
search To Develop an Intrinsically Safe 
Monitoring System for Coal Mines. Paper 



in Proceedings of the Fifth West Virginia 
University Conference on Coal Mine Elec- 
tro technology (Morgantown, WV, July 30- 
31, Aug. 1, 1980). West Virginia Univ., 
Morgantown, WV, 1980, pp. 20-1 to 20-11. 

4. Scott, L. W. Remote Monitoring of 
Air Quality in Underground Mines. Bu- 
Mines RI 8253, 1977, 14 pp. 

5. Purtell, L. P. Low Velocity 
Performance of Anemometers (contract 
H0166198, NBS). NBSIR 79-1759, May 1979, 
169 pp. 



12 



APPENDIX. —SPECIFIC BA4 AND VA216 DATA 



Tables A-l through A- 5 show the 0° yaw, 
0° pitch calibration data for the BA4 
9050 and 9061. 



TABLE A-l. - Calibration l 1 
BA4 9050, horn on 



of 



Figure A-l is a plot of pulse frequency 
versus true velocity (VA216) from NBS 79- 
1759 data and tables H-l through H-5 (5). 

TABLE A-2. - Calibration 2 1 of 
BA4 9050, horn on 



V + , m/s 



i » 



m/s 



SCALE 2 



SCALE 3 



V t /V| 





SCALE 1 




0.307 


0.10 


3.07 


.490 


.41 


1.20 


.994 


.90 


1.10 


1.52 


1.50 


1.01 


1.95 


2.00 


.976 



0.492 


0.30 


1.64 


.990 


.90 


1.10 


1.51 


1.45 


1.04 


1.96 


1.95 


1.01 


2.47 


2.50 


.989 


3.01 


3.20 


.941 


3.98 


4.40 


.904 


4.53 


5.00 


.906 



0.997 


0.90 


1.11 


1.51 


1.40 


1.08 


1.96 


2.00 


.979 


2.47 


2.50 


.989 


3.00 


3.10 


.968 


3.97 


4.30 


.925 


4.56 


5.00 


.913 


4.97 


5.50 


.904 


5.94 


6.50 


.914 


7.94 


8.60 


.924 


9.38 


10.00 


.938 



'Dropout speed, increasing = 
0.307 m/s; dropout speed, de- 
creasing = 0.300 m/s; pressure = 
744 mm Hg; temperature = 22.7° C. 



r t» 



m/s 



i » 



m/s 



SCALE 2 



SCALE 3 



V + /V 





SCALE 1 




0.302 


0.27 


1.12 


.505 


.46 


1.10 


1.01 


.93 


1.09 


1.52 


1.48 


1.03 


1.98 


2.00 


.990 



0.503 


0.40 


1.26 


1.02 


.95 


1.07 


1.52 


1.48 


1.02 


1.95 


2.00 


.976 


2.49 


2.55 


.977 


2.97 


3.10 


.956 


3.72 


4.00 


.931 


4.56 


5.00 


.912 



1.01 


0.98 


1.03 


1.52 


1.50 


1.01 


1.96 


2.00 


.982 


2.50 


2.60 


.960 


2.97 


3.20 


.928 


3.71 


4.05 


.916 


4.59 


5.00 


.918 


5.36 


5.90 


.908 


7.42 


7.90 


.939 


9.54 


10.00 


.954 



dropout 
0.302 m/s; 
creasing = 
760 mm Hg; 



speed, inc 
Dropout s 
0.284 m/s; 
temperature 



reasing = 
peed, de- 
pressure = 
= 20.2° C. 



13 



TABLE A-3. - Calibration 1 of BA4 9050, 
horn removed 



TABLE A-4. - Calibration 1 of BA4 9061, 
horn on 



V + , m/s 



Vj , m/s 



V + /Vj V+, m/s 



i > 



m/s 



V+/V, 





SCALE 1 




0.295 


0.26 


1.13 


.508 


.46 


1.10 


1.02 


.92 


1.11 


2.03 


2.00 


1.01 





SCALE 2 




0.516 


0.45 


1.15 


1.02 


.90 


1.13 


2.02 


2.00 


1.01 


3.08 


3.10 


.992 


4.91 


5.00 


.981 





SCALE 3 




1.03 


0.98 


1.05 


2.02 


2.00 


1.01 


3.07 


3.10 


.981 


4.90 


5.00 


.980 


7.02 


7.05 


.996 


10.20 


10.00 


1.02 



'Dropout speed 
dropout speed, 
pressure = 751 
21.2° C. 



320 



, increasing = 
decreasing = 
mm Hg ; temp 



0.295 m/s; 
0.289 m/s; 
erature = 



280 



240- 



200- 



>- 

UJ 

o 




160 



120 



200 400 600 800 1,000 1,200 1,400 



FIGURE A-l. - Pulse frequency versus true 
velocity for VA216. 





SCALE 1 




0.275 


0.22 


1.25 


.493 


.42 


1.17 


1.02 


.90 


1.12 


1.50 


1.46 


1.03 


1.99 


2.00 


.993 



SCALE 2 



0.500 


0.35 


1.43 


1.00 


.90 


1.11 


1.49 


1.45 


1.03 


1.98 


1.95 


1.01 


2.51 


2.52 


.996 


3.03 


3.15 


.960 


3.98 


4.30 


.925 


4.58 


5.00 


.915 



SCALE 3 



1.01 


0.90 


1.12 


1.51 


1.40 


1.08 


1.98 


1.95 


1.01 


2.50 


2.55 


.979 


3.01 


3.10 


.972 


3.99 


4.25 


.938 


4.95 


5.30 


.933 


5.97 


6.35 


.940 


7.92 


8.20 


.966 


9.77 


10.00 


.977 



1 Dropout speed 
dropout speed, 
pressure = 755 
18.7 °C. 



, increasing = 0.275 m/s; 
decreasing = 0.261 m/s; 
mm Hg; temperature = 



TABLE A-5. - Additional calibration 1 
BA4 9061, scale 1, horn on 



of 



V + , m/s 


V| , m/s 


V + /V, 


0.286 


0.22 


1.30 


.361 


.30 


1.20 


.440 


.37 


1.19 


.510 


.43 


1.19 


.605 


.52 


1.16 


.692 


.61 


1.13 


.800 


.71 


1.13 


.902 


.81 


1.11 


1.02 


.90 


1.13 


1.28 


1.18 


1.09 


1.50 


1.45 


1.04 


1.80 


1.77 


1.02 


1.96 


2.00 


.981 



Pressure 
19.3° C. 



= 761 ram Hg; temperature = 



fiU.S. CPO: 1981-505-019/5087 



INT.-BU.OF MINES, PGH., PA. 27869 



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